This invention relates to the use of electrically conductive polymers in sensors for reactive gases and more specifically to the use of composites made of such polymers in such sensors.
Ever since the relatively recent discovery that certain polymers either had or could be made to acquire a high electrical conductivity, there has been much interest in commercial development of such polymers. These electrically conductive polymers could serve as substitutes for metals in a variety of applications requiring high electrical conductivity. Work has been done to develop the use of electrically conductive polymers in batteries, solar cells, semiconductors, electromagnetic shielding, and traditional wiring.
Extensive work has been conducted with a number of polymers including poly(phenylene), poly(phenylene sulfide), poly(phenylene oxide) and polyacetylene. Of the polymers which have been investigated, polyacetylene has shown the most promise up to the present time. Such polyacetylene is usually doped with suitable impurities such as iodine, AsF.sub.5 or HSO.sub.3 F, SO.sub.3, sodium, potassium and lithium to increase the conductivity. Such methods are discussed in U.S. Pat. No. 4,269,738 which was issued on May 26, 1981 to Pez and Anderson.
Many polymers are susceptible to degradation or disruption in the presence of air, moisture, and other agents, including ammonia, hydrogen sulfide, methane, chlorine and carbon monoxide. Polyacetylene and several other electrically conductive polymers are no exception. The reactivity of these polymers leads to their instability and thus has created a need for methods or additives to decrease this tendency to be unstable. A variety of methods have been tried including chemical doping, ionic implantation, antioxidizing agents, and blending with a protecting polymer. The present invention uses the instability of such polymers to provide a reactive gas sensor.